Revert of Remove WebElement::hasTagName. (https://codereview.chromium.org/354763002/)

Reason for revert:
Broke Android build.


Original issue's description:
> Remove WebElement::hasTagName.
> 
> There are no callsites in Chromium.  This function is unsafe because it
> ignores namespace URI.
> 
> BUG=
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=176895

TBR=keishi@chromium.org,isherman@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/350433004

git-svn-id: svn://svn.chromium.org/blink/trunk@176906 bbb929c8-8fbe-4397-9dbb-9b2b20218538